Surface treatment by particulate abrasion is an old and valuable process. This is done in primarily two forms: the first involves the application of direct physical pressure on the particulate media and rubbing the media across the target surface, e.g., grinding, sanding, polishing, etc.; and the second generally involves the blasting of the target surface with air-entrained particulate media, e.g., sandblasting, grit blasting, etc.
Sandblasting technology has been used for a number of years to decorate the surface of articles in a predetermined pattern. To achieve this decoration, particulate abrasive media such as steel grit, slag, sand and other forms of silicone oxide, and aluminum oxide are propelled at high velocities against the target surface. In order to control the areas of the target surface which are actually abraded by the blasting media, a patterned mask is applied to the surface. In the past, such masks were prepared manually from rubber, paper, or other material which could withstand penetration by the abrasive media, and they were applied to the target surface using an adhesive, carefully applied to the mask itself. Any adhesive which extended into the void areas of the mask were detrimental, as it often acted as an extension of the mask. This adhesive extension of the mask results in inaccuracies in the etched pattern produced by the sandblasting.
A more recent innovation in sandblasting operations is the use of photoimageable masks or photoresists. These photoresists comprise a photosensitive polymeric material which, upon selective exposure to light of a particular wavelength range, forms regions of two distinct types: those which are removable by a developer liquid and those which are unaffected by the developer. These removable and unremovable regions then form void areas and mask areas after developing. When the photoresists is applied to a target surface, the void areas allow the particulate abrasive media to strike the target surface, while the mask areas protect the underlying target surface from the particulate media.
There have been a number of different approaches to the problem of attaching the photoresist to the target surface. One approach is exemplified by Nakamura et al., U.S. Pat. Nos. 4,456,680 and 4,587,186 wherein the photoresist itself exhibits pressure sensitive adhesive properties. However, this approach requires the use of a liquid photosensitive material and careful preparation of the pressure sensitive adhesive photoresist. This involved preparation of the photoresist requires the user to be rather sophisticated and essentially precludes the use of the technology by small job shops.
Another approach requires the use of a liquid pressure sensitive adhesive forming composition which can be applied to the photoresist mask as a discrete layer. Again, if these pressure sensitive adhesive products are not carefully applied to the photoresist, they can act as a photoresist themselves as discussed above. Therefore, great accuracy is needed in the application of these adhesives to the photoresist to avoid overshoot of the adhesive into the void areas of the photoresist. In order to achieve this accuracy, especially in applications requiring very fine photoresists, time consuming manual application of the adhesive or an expensive adhesive application machine is required.
In addition, there are several products available on the market for general use in graphic arts. These adhesives are useful for application of photoresist masks or general mounting of graphic arts materials and include elastomer based products such as 3M PHOTO MOUNT adhesive, available from 3M Co., and CAMIE 350, available from Camie Campbell, Inc. However, these adhesive compositions also are less than desirable. While, with the proper application weight, these adhesives may be penetrated and removed by the blasting media where exposed by the mask, the adhesives are not water redispersible. Therefore, to remove the sandblasting masks after the blasting operation, hazardous solvents are needed.
In view of the current state of the sandblasting adhesive art, there are a number of failings visible. Therefore, a new pressure sensitive adhesive useful to adhere sandblast masks having very high resolution to target surfaces is needed which is easy to use, versatile, blastable, and water redispersible. Such an adhesive would avoid the need for using great care and accuracy in the application of the adhesive and using hazardous organic solvents to remove the mask after blasting.